The invention relates to an expansion screw for regulating teeth, having two expansion-screw bodies, the spacing between which can be changed by means of a spindle, and having at least one guide pin which is aligned parallel to the spindle and engages in guide openings of the two expansion-screw bodies, the spindle having a first and a second threaded portion, each of which is connected to an expansion-screw body, and an actuating portion, with at least one point for application of a tool for rotating the spindle, and the expansion screw having a locking mechanism which interacts with the actuating portion in order to secure the spindle against unintended rotation.
An expansion screw of this kind is known from DE-A-10 2007 002 040. Rotating the spindle makes it possible to change the spacing which the two expansion-screw bodies assume in relation to one another, and the locking mechanism ensures that the spindle does not adjust of its own accord. The locking mechanism used in the known expansion screw is a metal strip which extends over the spindle, transversely to the longitudinal axis of the spindle, and is secured to the guide pins. It rests on the outer periphery of the actuating portion and acts as a friction brake, which makes it more difficult for the spindle to rotate. The actuating portion has a non-circular outer cross-section, so that the frictional force generated by the metal strip depends on the angle-of-rotation position of the spindle. The spindle can thus be secured against unintended rotation, but the expansion screw has not insignificant installation dimensions.
It is an object of the present invention to develop an expansion screw of the type mentioned in the introduction such that it has smaller installation dimensions.